Small Craft Advisory 91, NWS Medford, OR

Area Forecast Discussion
National Weather Service Medford OR
948 AM PST Mon Nov 19 2018

.Updated Aviation Discussion.

.DISCUSSION...Another day of quiet, stagnant weather is on tap today.
Air quality observations suggest degraded air quality under this
ridge of high pressure, and our Air Stagnation Advisory continues
through tonight for the East Side and coast...and through Tuesday
night for West Side Valleys. After that, our atmosphere will be
well-mixed, and there will be no Air Stagnation concerns.

Weather will become more interesting tomorrow as winds ahead of a
front increase at the coast, East Side, and especially in the Shasta
Valley. Then, rain and high mountain snow arrives Wednesday.

In addition to expected high mountain pass snowfall, we do want
people who plan on traveling ahead of, during, and after
Thanksgiving to be aware of the potential for slick roadways after
weeks of dry weather. Slow down and be safe.

Please see the previous discussion for more details about the
weather pattern change.

&&

.AVIATION...For the 19/18Z TAFs...A similar pattern to what's
occurred over the past few days will continue through the TAF
period. Along the coast, the Coquille Valley and Umpqua Basin,
marine stratus with IFR to LIFR ceilings should improve to VFR 21z.
However it's possible Co In the Umpqua Basin, LIFR fog burn off LIFR
ceilings could linger longer at Roseburg until 22z. Marine stratus
with LIFR ceilings/visibility will return this evening. Elsewhere,
VFR conditions will continue through the TAF period, however could
not rule out patchy fog in the Illinois Valley and Grants Pass area
towards daybreak Tuesday. -Petrucelli

&&

.MARINE...Updated 230 AM PST Monday 19 November 2018...Light winds
and seas will persist into early Tuesday. A cold front will pass
through the waters Tuesday night into Wednesday with gusty south
winds, rain, and steep seas. A stronger front will move through on
Thursday and may bring south gales. High west swell is likely to
follow Thursday night into Friday, and may become very high at 16 to
20 ft during a likely peak late Thursday night. -DW

&&

.PREV DISCUSSION... /Issued 424 AM PST Mon Nov 19 2018/

DISCUSSION...In spite of the date and the approaching wet weather
approaching mid week conditions remain very unseasonably dry until
the rain rolls in Tuesday night into Wednesday. This will make for
any fires, even barrel burning, to be potentially hazardous right
up until the rain moves in. Increased winds as the front
approaches will increase the possible danger.

If you want to burn, wait until mid week after the rains have
begun, don't be "that person"!

Models continue to show precipitation moving onshore Tuesday
night. Ahead of it the gradient is tightening from Redding to
Medford and gusty winds increasing from the south in the Shasta
Valley. Gusty Shasta valley winds will spill over a bit into the
south end of the Shasta valley and as the rain moves in the
Medford area should be mostly in a rain shadow with downslope
flow until Wednesday afternoon. As we really don't see a good BL
flow feeding moisture ahead of this front, wouldn't be surprised
if the actual precip is well below what the models are currently
indicating. With the moderate southerly flow, snow levels should
remain above pass levels through Wednesday night until the 700 mb
flow becomes more westerly. Thursday morning will see snow level
drop briefly to near the Cascade passes. Sven

PREVIOUS LONG TERM...Wednesday through Saturday...

*Travel delays will be possible for the Thanksgiving holiday
starting Wednesday through the weekend.
*Snow expected on the highest passes, including highway 140 near
Lake of the Woods and the Diamond Lake Junction on Thursday and
Friday. Snow levels are expected to be near, but higher than
Siskiyou Summit.
*Windy conditions could make travel difficult for high profile
vehicles east of the Cascades and along the coastal highways.

Wednesday is going to mark the beginning of a drastic pattern
change, just in time for the Thanksgiving holiday and the weekend
afterward. We are expecting several fronts to come through and bring
moderate precipitation to the coast, the coastal range, and the Mt.
Shasta area. The first front on Wednesday is expected to be the
weakest of the three fronts, which will have to work to break down
the area of high pressure that is currently over the Pacific
Northwest. This will bring mainly breezy to gusty winds east of the
Cascades and at the coast.

The second front will arrive on Thursday, and will be much stronger.
The ECMWF model has come more in line with the GFS and are
indicating the moderate to brief periods of heavy precipitation
across the aforementioned areas. The timing of the system still
needs to be ironed out, but the major models and ensembles are
zeroing in on Thursday evening.

The big question is going to be what happens with the snow levels
and snow. We are expecting snow across the Cascades and the higher
peaks of the Siskiyous. This includes Mt. Ashland. For the Mountain
passes, the snow levels will be around 5000 to 6000 feet on
Wednesday and lower to near 4500 feet for Thursday night into
Friday. This means that we are expecting snow on our highest passes,
including Highway 140 near Lake of the Woods, Diamond Lake junction
area. Although we are expecting snow levels to be higher than
Siskiyou Summit, it is worth noting that this is in the extended
forecast; so confidence is only so-so.

The next front will arrive Friday into Saturday and continue into
the weekend. The system will be a bit weaker, so the precipitation
is not expected to be as strong. Overall, if this forecast verifies,
these systems will quickly bring southern Oregon and northern
California back to near normal precipitation and snowfall for
November. Thus, it is recommended to keep an eye on the forecast for
updates. -Schaaf

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Air Stagnation Advisory until 4 AM PST Tuesday for ORZ021.
     Air Stagnation Advisory until 4 AM PST Wednesday for ORZ023.
     Air Stagnation Advisory until 4 AM PST Tuesday for ORZ024>031.

CA...None.

Pacific Coastal Waters...None.